Amorphous metals or metallic glasses have unique properties such as superior resistance to corrosion and wear. Unfortunately, such metallic glasses are extremely limited in their usefulness because they can only be produced in the form of very thin foils or powder. Commercially available amorphous metal strips can be obtained with a thickness of less than 0.003 centimeters. If a means could be provided to bond amorphous metals to thicker crystalline metal substrates, unique products having superior resistance to corrosion and wear and extraordinary tensile strength would be produced.
Currently, materials having generally superior strength and corrosion resistance and high tensile strength can be produced from abundant metals such as iron with the addition of lesser amounts of critical and strategic metals such as cobalt. The use of an amorphous metal layer on an abundant metal as a substitute for those currently produced materials would conserve the critical and strategic metals from which they must be made and reduce dependence on foreign sources for these strategic metals.
A number of methods have been used in the prior art to bond or coat metallic glasses to metal substrates. For example, explosive cladding has been used to bond metallic glasses to a metal substrate. Unfortunately, this is an expensive and specialized procedure warranted by only a few applications. The adiabatic heating associated with this process, and the limited ductility of many glassy alloys, places additional limitations on this procedure. Another method of bonding metallic glasses to metal substrates is sputtering and ion plating. While this technique can provide a glassy coating with good corrosion resistance, the thickness of the coating is usually limited to a few hundred microns. In addition, the use of specialized equipment is required. Electrodeposition has also been used to bond a metallic glass to a metal substrate. However, the deposits formed have not been very corrosion resistant.
Besides the methods mentioned above to bond a metallic glass to a metal substrate, laser glazing has also been used. According to this procedure, a laser on a rotating metallic specimen is used to make a glassy surface layer. The thickness of the glassy layer formed is only about 50 microns, and glassy products are only produced on specialized alloys. Ion implantation techniques are also suitable to bond metallic glasses to metal substrates. However, only thin coatings of 60 microns or less have been produced. In addition, this procedure often results in the formation of microcrystalline materials depending on the alloy used.
Although the above methods can produce a bonding of a metallic glass to a metal substrate, these methods are of limited use and are more effective in producing microcrystalline layers on the crystalline metal rather than glassy surfaces. In addition, the thickness of the metallic glass is severely limited.
The use of conventional hot rolling procedures to clad a metallic glass to a metal substrate has been explored and found to be unworkable. This conclusion is stated in an article entitled "New Class of Corrosion Resistant Coatings" by R. B. Diegle appearing in SAMPE QUARTERLY, January, 1982, pages 26-30. In this article, it was found that conventional hot rolling procedures caused the glassy metals to crystallize and/or undergo embrittlement.